Research Question: What is the average mercury content in swordfish in the Atlantic Ocean?
Research Question: What is the average mercury content in swordfish in the Atlantic Ocean?
Key point: Statistics are calculated from a sample, while parameters are properties of the entire population.
A recent article in a college newspaper stated that college students get an average of 5.5 hours of sleep each night. A student who was skeptical about this value decided to conduct a survey by asking 25 randomly-chosen students about their sleep habits. On average, the surveyed students slept 6.25 hours per night.
An example of faulty reasoning:
A man on the news got mercury poisoning from eating swordfish, so the average mercury concentration in swordfish must be dangerously high.
Research Question: Over the last five years, what is the average time to complete a degree for Duke undergrads?
Research Question: Over the last five years, what is the average time to complete a degree for Duke undergrads?
We can easily access ratings for products, sellers, and companies through websites. These ratings are based only on those people who go out of their way to provide a rating. If 50% of online reviews for a product are negative, do you think this means that 50% of buyers are dissatisfied with the product? Why or why not?
Recall:
Key Point: The only difference between the groups should be the treatment under consideration.
Data where no treatment has been explicitly applied (or explicitly withheld) is called observational data.
Group Discussion: Suppose an observational study tracked sunscreen use and skin cancer, and it was found that the more sunscreen someone used, the more likely the person was to have skin cancer. Does this mean sunscreen causes skin cancer? Can you identify a possible confounding variable?
In one 2009 study, a team of researchers recruited 76 volunteer subjects and divided them randomly into two groups: treatment or control. One group was given 25 grams of chia seeds twice a day, and the other was given a placebo that looked like chia seeds, but that had no nutritional value. After 12 weeks, the scientists found no significant difference between the groups in appetite or weight loss.
What type of study is this?
What are the experimental and control treatments in this study?
Has blinding been used in this study?
If the researchers had found a significant difference, could they have made a causal statement?
Can we generalize the conclusion to the population at large?